The present invention relates to sensor technology, and in particular, to sensor technology for detecting angular displacement or bending. Even more particularly, the present invention relates to electrical sensors in which the value of the conductance/resistance and/or conductivity/resistivity of the sensors changes with angular displacement or bending. One application of the present invention would be, for example, to detect the amount of angular displacement or bending of body parts, for example, bending of arms, legs, and fingers of the human body, although other applications may also be found.
Various techniques for determining displacement, deformation or elastic elongation using measurement of resistance, conductance, resistivity or conductivity are known. For example, U.S. Pat. No. 4,748,433 to Jackson et al discloses an electro-conductive elastomer device capable of providing sensory signals representative of elastic elongation.
U.S. Pat. No. 4,444,205 to Jackson shows a device for assessing joint mobility, for example, of human or animal joints.
U.S. Pat. No. 4,715,235 to Fukui et al discloses a deformation sensitive electroconductive knitted or woven fabric.
U.S. Pat. No. 4,639,711 to Edholm et al discloses a deformation sensitive signal transmitter for electric signals which comprises an elastic body consisting of an elastomer matrix containing carbon black as a filling agent.
U.S. Pat. No. 3,820,529 to Gause et al discloses a conductive elastomeric extensometer for measuring surface area changes of the human body.
U.S. Pat. No. 4,273,682 to Kanamori discloses a pressure-sensitive electrically conductive elastomeric composition comprising a substrate composed of an organic flexible material and electrically conductive particles. The composition has such a characteristic that the electric resistivity is reduced under application of pressure.
U.S. Pat. No. 4,252,391 to Sado, U.S. Pat. No. 4,258,100 to Fujitani et al and U.S. Pat. No. 4,152,304 to Tadewald each disclose various pressure-sensitive electrical materials.
U.S. Pat. No. 4,729,809 to Dery et al discloses a conductive adhesive composition.
U.S. Pat. No. 3,332,280 to Fish et al discloses a strain gauge using an electrolyte filled tube for measuring extensions and U.S. Pat. No. 4,461,085 to Dewar et al discloses a goniometer using mercury-in-rubber sensors for use in measuring angular movements of joints of a human or animal body.
U.S. Pat. No. 4,038,867 to Andrews et al discloses a transducer assembly for measuring loads in flexible sheet material and U.S. Pat. No. 3,878,711 to Randolph, Jr. discloses an extensometer comprising an electromechanical deflection sensor mounted in the extensometer to bend or deflect proportionately with the relative movement of the end portions of the device.
U.S. Pat. No. 3,174,125 to Curby discloses a mechanical pressure sensor and U.S. Pat. No. 3,958,455 to Russell discloses a force transducer for a strain gage of the resistance wire type.
U.S. Pat. No. 3,971,250 to Taylor discloses an electret sensing medium having plural sensing units which may be used as a bending stress sensor.
U.S. Pat. No. 4,023,054 to Taylor discloses a strain sensor employing piezoelectric material, U.S. Pat. No. 3,888,117 to Lewis discloses an electromechanical pressure sensor, U.S. Pat. No. 4,429,580 to Testa et al discloses a stress transducer for fabrics and flexible sheet materials, and U.S. Pat. No. 4,258,720 to Flowers discloses a strain gauge plethysmograph.
In addition to the use of conductive material which change resistance or conductivity due to physical movement such as angular displacement, or various electromechanical and transducer arrangements, other types of sensors for determining displacement, bending, flex or other physical parameters such as deformation and stress are known.
For example, U.S. Pat. No. 4,542,291 to Zimmerman discloses an optical flex sensor which may be used to determine the amount of bending, for example, of a finger of the human hand.
U.S. Pat. No. 4,414,537 to Grimes discloses a digital data entry glove interface device which utilizes sensors disposed on a glove positioned with respect to the hand for detecting the flex of finger joints. The flex sensors, as shown in FIGS. 4 and 5 of that reference are optical in nature, relying upon the constriction of a tube in order to determine the amount of flex. Furthermore, the flex sensor of that reference is primarily a digital device, since it is incapable of determining further flexure beyond a given point when the optical tube is completely closed off by the flexure.
The flex sensor of the Zimmerman patent, U.S. Pat. No. 4,542,291, utilizes a flexible tube having an interior wall covered with a reflective material and uses a combination of reflected and direct light received at the receiver to determine the amount of flex. However, the flex sensor of that reference also suffers from an inability to determine accurately the amount of flex beyond a given point.
U.S. Pat. No. 4,269,506 to Johnson et al discloses an apparatus for measuring the influence of physical parameters such as temperature, pressure and force on the length of a path. This system uses an elastically stretchable optical fiber to determine length changes based upon travel times through the optical fiber.
U.S. Pat. No. 4,420,251 to James et al discloses an optical deformation sensor which is responsive to, for example, fatigue, vibration, flex, torsion, bending or slippage.
U.S. Pat. No. 4,123,158 to Reytblatt discloses a photoelastic strain gauge
U.S. Pat. No. 4,191,470 to Butter discloses a laser-fiber optic interferometric strain gauge
U.S. Pat. No. 3,517,999 to Weaver discloses an optical strain gauge
U.S. Pat. No. 3,229,511 to Rossire discloses an optical stress sensor for an aircraft.
None of the above sensors have provided a simple, reliable means for accurately measuring, over a wide range of values, angular displacement or bending, for example, of human joints such as finger joints.